The present invention relates generally to aircraft, and more specifically the invention pertains to a variable geometry lighter-than-air craft which can change from a buoyant airship to a heavier-than-air craft by changing shape. The craft has a flexible envelope filled with helium or other lifting gas. Releasing or tightening the adjusting lines changes the envelope shape by adjusting the internal dimensions and extending or withdrawing wing expansion sections. The craft's shape can change from an ovoid shape for lighter-than-air flight to a winged shape for heavier-than-air flight. Controlling the craft's shape regulates the buoyant lift. Controlling the craft's speed and trim regulates the aerodynamic lift.
Since time immemorial, man has sought to design and build the optimum flying machine. Reduction of moving parts is part of such optimization. During the Middle Ages, various inventors designed apparatus which they felt would achieve the objective of enabling an to fly. It has, however, only been within the last 100 years that significant progress has been made toward developing viable aircraft.
Basically, flying craft can be divided into one of two types: lighter-than-air devices and heavier-than-air devices. Developments came earlier with regard to the former type of craft. Such a vehicle is provided with a bladder or balloon which can be filled with a gas having a specific gravity less than that of air. This type of craft is an application of Archimedes' principle which states that a body immersed in a fluid is bouyed up by a force equal to the weight of the liquid it displaces. If the weight of the fluid displaced is greater than the weight of the body, the body will "float" on the fluid. Zeppelins and hot air balloon recreational craft are illustrative of this type of vehicle.
Heavier-than-air craft, on the other hand, function because of Newton's third law of motion and Bernoulli's principle. Newton's third law of motion states that, for every action, there is an equal and opposite reaction. A helicopter is a heavier-than-air craft illustrating the application of this law. As the main rotor of a helicopter rotates, the pitch of the blades will cause the exertion of a force upon the air through which the rotor cuts. As a consequence, an equal and opposite force will be exerted upon the rotor blades as they rotate. This force will, in view of the pitch of the rotor blades and the direction in which the rotor rotates, urge the helicopter upwardly.
Lighter-than-air vehicles can remain aloft indefinately and are capable of touching down in areas which would be inaccessible for most other conventional transport vehicles. They can be powered by a simple propeller engine and refueling can be accomplished either directly from the ground or by means of a simple umbilical cord from another aircraft.
People have been reticent since the later 1930's to pursue flight by lighter-than-air vessels, after the "Hindenburg" was mysteriously and spectacularly consumed by flames. However, recent developments require airborne platforms for large sensor, systems such as phased array radars operating at frequencies between 0.5 and 2 GHz. For air surveillance and tracking, this means large antennas about 60 ft by 200 feet in size. All directional coverage requires at least three such antennas oriented at 120 degrees from each other.
Operational requirements for such systems indicate that the platform must be able to remain on station for over 24 hours. A low speed platform can enhance low altitude radar target detection in clutter. However, operational flexibility requires a higher speed dash capability. Altitude requirements range from 10,000 feet to 45,000 feet for adequate radar coverage against low altitude.
Solutions to the large, long endurance airborn platform problem include:
large aircraft (e.g. Boeing 747, C-5, C-17, etc.); PA1 aerobody (flying wing or lifting body) aircraft; and PA1 airships (dirigibles, blimps, etc.). However each has some disadvantages, explained below.
Large aircraft cannot carry the three large phased array radar antennas required for all directional surveillance. They also must operate at high speeds which is undesirable for clutter suppression. They have limited endurance.
Aerobody aircraft are a solution to carrying three large antennas by enclosing them in an airfoil. However, aerobodies need higher airspeeds at high altitudes, which limits their endurance. Aerobodies do not have good lift to drag ratios compared to conventional aircraft.
Airships can carry large size phased array antennas and have good endurance at low speeds and altitudes. They are limited in altitude by their weight and volume because they are buoyant. Practical airship altitudes are limited to about 15,000 feet and maximum air speed is limited to about 100 knots.
The variable geometry airship is a way to change an airship into an aircraft which is supported by both buoyancy and aerodynamic lift, sometimes called a hybrid LTA aircraft. Changing shape permits higher aircraft speeds and better altitude at the expense of endurance.
The task of providing a variable geometry airship which can change from a fully buoyant airship into winged aircraft while in flight is alleviated, to some extent, by the systems disclosed in the following U.S. Patents, the disclosures of which are specifically incorporated herein by reference:
U.S. Pat. No. 3,907,218 issued to Miller; PA0 U.S. Pat. No. 3,913,871 issued to Miller; PA0 U.S. Pat. No. 3,970,270 issued to Pittet; PA0 U.S. Pat. No. 3,976,265 issued to Doolittle; PA0 U.S. Pat. No. 3,993,268 issued to Moore; PA0 U.S. Pat. No. 4,052,025 issued to Clark et al; PA0 U.S. Pat. No. 4,085,912 issued to Slater; PA0 U.S. Pat. No. 4,102,519 issued to Crosby; PA0 U.S. Pat. No. 4,261,534 issued to Roselli; PA0 U.S. Pat. No. 4,366,936 issued to Ferguson; PA0 U.S. Pat. No. 4,482,110 issued to Crmmins; PA0 U.S. Pat. No. 4,497,272 issued to Veazey; PA0 U.S. Pat. No. 4,779,825 issued to Sams.
U.S. Pat. No. 4,695,012 issued to Lindenbarium; and
The Miller patents disclose heavier-than-air aircraft that have lighter than air compartments. The Pittet patent discloses a low speed aircraft with an airfoil capable of serving as a lighter-than-air system or a heavier-than-air system.
The Doolittle reference disclosed a semibuoyant composite aircraft that resembles a helicopter with a rotating balloon sphere encompassing the axis of its rotors. The Moore patent is a ballooned stol aircraft.
The semi-buoyant aircraft of the Clark et al. patent is a fixed-wing aircraft which encloses pressurized buoyant cells. The Slater patent discloses a convertible airship with rotataly mounted wing structures.
The Crosby patent discloses a variable lift inflatable airfoil for tethered balloons. The Roselli patent resembles that of Crosby in that it disclosed an inflated wing aircraft.
The Ferguson patent discloses an aircraft which uses a spherical balloon which is pressurized to prevent its changes in geometry. The Crimmins patent discloses a cyclorotor composite aircraft which uses a combination of a lighter-than-air compartment (for bouyant lift) and a system of rotating airfoils to provide lift.
The Veazey references disclosed a system of inflatable mastless sails which are used on a boat or a ship. The Lindenbaum patent discloses an aerial load-lifting system which used a lighter-than-air blimp with a heavier-than-air helicopter system. The Sams patent describes a propelling rotor which may be rotated about an axis. The Veazey, Lindenbaum and Sams patents are included because they provide descriptions of the technology which may be used by the present invention the details of which are discussed in the detailed description that follows.
While the above cited references are instructive, there remains a need for a variable geometry lighter-than-air craft which can change from a buoyant heavier-than-air craft by changing shape. The present invention is intended to satisfy that need.